It is planned during the next year to determine the type of iron- sulfur structure present in several complex iron sulfur proteins such as hydrogenase and nitrogenase. In addition we wish to determine what role molybdenum plays in reduction of dinitrogen by nitrogenase, i.e., whether it is involved in electron transfer to substrate, ATP hydrolysis or both. This information will be sought using a new technique developed by inorganic chemists and physicists for exchanging sites intact from more complicated large molecules to simple identifiable compounds as well as obtaining information concerning the metal constituents by x-ray analysis. In addition it is planned to determine the fate of molybdenum required by cells of dinitrogen fixing organisms and supplied as MO2 minus sub 4. We want to know how it enters the cell, to what form is it converted when it enters the cell and how it is transferred and incorporated into nitrogenase.